1. Field of the Invention
This invention relates generally to a vertically integrated electronically steered phased array and, more particularly, to a vertically integrated electronically steered phased array that is synchronized to a global clock signal applied to a local oscillator from a tunable phase-locked loop (PLL) in each channel of the array.
2. Discussion of the Related Art
Transceiver arrays are widely used in wireless communications, radar applications and sonar applications. A transceiver array is an array of transceiver channels each including an antenna where the channels combine to provide a directional beam for both transmitting and receiving purposes, including beam scanning. As the directivity of the array increases, the gain of the array also increases.
Various types of transceiver arrays are known in the art that provide beam steering. One known transceiver array type includes mounting individual transceiver front-end channels on a mechanical device that moves to provide beam steering or scanning.
Another known transceiver array type is a phased array. A typical phased array includes an antenna in each channel that is connected to a phase shifter, and a power combiner for adding the signals together from the antennas. The phase shifters control either the phase of the excitation current of the antenna for transmission or the phase of the receive signals. When the signals are combined, a beam is formed in a particular direction. Particularly, a transmit beam is formed in space, and a receive beam adds coherently if the signals are received from a particular region of space. The radiation pattern of the transceiver array is determined by the amplitude and phase of the current at each of the antennas. If only the phase of the signals is changed and the amplitude of the signals is fixed, the beam can be steered.
Another type of transceiver array that has been developed in the art employs digital beamforming systems that eliminate the need for the phase shifters to provide beam steering. The digital beamforming systems digitally provide beam steering. One advantage of digital beamforming is that once the RF information from each channel is captured in the form of a digital stream, digital signal processing techniques and algorithms can be used to process the data in the spatial domain.
Digital beamforming is based on the conversion of the RF signal at each antenna into base-band signals. The beamforming is provided by weighting each digital signal from the channels, thereby adjusting their amplitude and phase so that when they are subsequently added together in post-processing they form the desired beam. Thus, the linear phase weight applied to the digitized signal at each channel can make the antenna beam appear as if it is steered to different angular directions.